Lumbosacral transitional segments: Classification, prevalence, and effect on disk height

Objective: To determine the rate of lumbosacral transitional segments among chiropractic practice settings and to determine if this anomaly would affe ct the height of the lumbosacral disk. Study Design: Retrospective review of radiographs. Setting: Los Angeles College of Chiropractic outpatient clinic and a privat e chiropractic office. Samples: A total of 20 lumbar series with lumbosacral transitional segments from a private chiropractic office, 47 lumbar series with lumbosacral tran sitional segments, and 60 age- and sex-matched control series fi om a colle ge clinic. Results: A total of 2.3% of 882 lumbar series at the private chiropractic o ffice and 6.5% of 786 lumbar series at the Whittler Health Center showed lu mbosacral transitional segments of types II, III, or IV. The L5-S1 interver tebral disk height was significantly smaller in patients with lumbosacral t ransitional segments compared with those without (ie, 11% vs 19% of total l umbar disk height, respectively). When bilateral bony fusion of L5 to the s acrum was present, the L5-S1 disk height was significantly smaller than tha t without bony fusion (ie, 8% vs 12% to 14% of total lumbar disk height, re spectively). Conclusions: We conclude that the rare of is low in chiropractic practice. Tn the presence of occurrence of lumbosacral transitional segments lumbosac ral transitional segments, especially when there was bony fusion, the lumbo sacral intervertebral disk was significantly narrower than the upper lumbar disks, which should not be considered as disk degeneration or displacement . The type of lumbosacral transitional segment present also showed a signif icant effect on the height of the lumbosacral disk.